Inorganic fine particles having an “up-conversion” function of converting long wavelength light such as infrared rays to short wavelength light such as visible light or ultraviolet rays are expected to be used for medical purposes as biomarkers or the like. Recently, a highly functionalized material including a matrix material in which such inorganic fine particles are dispersed to impart an up-conversion function has been drawing attention.
Known examples of the inorganic fine particles having an up-conversion function include those mainly containing lanthanoid elements. For the up-conversion function, a phenomenon called “multiphoton excitation” derived from the energy level difference of these elements is utilized.
Irradiation of glass containing lanthanoid elements with infrared rays is known to generate up-conversion fluorescence within a visible region on a short-wavelength side. For example, Patent Literature 1 discloses that up-conversion glass containing a heavy metal oxide (e.g., TeO2, Ga2O3, PbO, Bi2O3, GeO2) and Er2O3 as a rare earth element oxide can provide emission of light having a peak at around 560 to 565 nm.
Patent Literature 2 discloses a laminated glass comprising two transparent plates and a hydroxy terephthalate-containing intermediate layer interposed between the transparent plates. Such a laminated glass can display information when irradiated with specific light.
Use of exciting ultraviolet laser as irradiation light, however, has a problem of safety.